The invention describes a thick film getter composition for use in controlling moisture. Many environments are susceptible to unwanted moisture and this is especially so in the case of various electronic devices.
In an effort to control unwanted moisture, the concept of using a getter has been known for many years. Getters are substances which are added to a system or mixture to consume or inactivate traces of impurities.
One approach to minimizing the deleterious effects of moisture has involved the enclosure of moisture sensitive devices in a barrier to separate the active materials from oxygen and moisture. This approach has had some success, but it does not always adequately address the problems caused by even those small amounts of moisture trapped within the enclosure or diffusing into the enclosure over time.
The use of getters for controlling moisture within a sealed enclosure for an electronic component or device is well known. These sealed enclosures are designed to protect sensitive electronic components and devices from the outside environmental contaminants, including moisture. However, some electronic devices are highly sensitive to moisture and require moisture control to very low levels. At the same time, these electronic devices require that the getter composition be easily applied and processed while demonstrating that the processed composition sufficiently adheres to the desired substrate. The present invention provides a UV-curable composition to accommodate these requirements.
The prior art materials associated with getters and their use in electronic applications have been described below. Typically, the getter materials are not screen-printable compositions and are comprised of a desiccant material (i.e., zeolite, silica gel, etc.) and a binder. The binder may be organic or inorganic. The following illustrate the state of the prior art.
U.S. Pat. No. 5,244,707 to Shores discloses a sealed enclosure of an electronic device which incorporates a coating or adhesive with desiccant properties. The coating or adhesive comprises a protonated alumino silicate powder dispersed in polymer.
U.S. Pat. No. 5,591,379 to Shores teaches a composition of matter useful as a desiccant in a hermetic electronic device, comprising a powder dispersed in a binder, wherein said powder is selected from the group consisting of zeolite molecular sieves, activated alumina, silica gel, alkaline earth oxide, and alkali metal carbonate; said binder is a continuous matrix of porous glass or porous ceramic; and said powder to binder volume ratio is 0.001-2. The glasses disclosed for use as a binder must be made porous by creating channels for water vapor to penetrate. This may be done by various techniques known in the art, such as the use of blowing agents, fast evaporation of water or other gases during formation, fast decomposition of metalloorganic polymers and low temperature or incomplete sintering.
U.S. Pat. No. 1,626,682 to MacRae discloses a multi-pixel flat panel display means which include spaced apart first and second electrodes, with a patterned solid material layer in contact with one of the electrodes, exemplarily between the two electrodes. The patterned layer (the web) includes a multiplicity of apertures, with at least one aperture associated with a given pixel. In the aperture is disposed a quantity of a second material, exemplarily, a phosphor in the case of a flat panel field emission display, or a color filter material in the case of a liquid crystal display. The web can facilitate second material deposition by means of screen-printing. The web also can facilitate provision of spacer structure between two electrodes, and can include getter or hygroscopic material.
U.S. Pat. No. 5,401,706 to Fischer teaches a process for making a desiccant-coated substrate capable of being used at temperatures over 150 degrees Fahrenheit, the desiccant being in the form of particles and the particles having pores and being adhered to the substrate by a binder, the coated substrate being sufficiently flexible and the coating having sufficient adherence to the substrate so that the coated substrate can be formed into corrugated shapes, the desiccant particles in the coated substrate having at least 60% of their original adsorption capacity and the binder having good breathability; said process comprising the steps: (a) forming an aqueous suspension comprising particles of one or more desiccants, a water-based organic binder, a suspending agent to help maintain the desiccant particles in suspension, and an organic pore-clearing agent at least some of which enters at least some of the pores of the desiccant particles; (b) depositing the suspension on the substrate; and (c) causing the binder of the deposited suspension to set so that the deposited desiccant particles adhere to the substrate and causing at least some of the pore-clearing agent to leave the pores of the desiccant particles to prevent the binder from occluding at least some of the pores of the adhered desiccant particles, thereby to form a desiccant-coated substrate capable of being used at temperatures over 150 degrees Fahrenheit and of sufficient flexibility and having a coating having sufficient adherence to the substrate so that the desiccant-coated substrate can be formed into corrugated shapes and in which the desiccant particles in the coated substrate have at least 60% of their original adsorption capacity and in which the binder has good breathability.
U.S. Pat. No. 6,226,890 to Boroson et. al, teaches a method of desiccating an environment surrounding a moisture-sensitive electronic device sealed within an enclosure. Boroson clearly states that the following desiccants will not “function effectively with highly moisture-sensitive devices at a humidity level lower than 1000 ppm:” alumina, bauxite, calcuim sulfate, clay, silica gel, zeolite, molecular sieves, and activated alumina.
U.S. Pat. No. 4,771,085 to Lazaridis, describes the use of curable dielectric compositions in membrane touch switch type circuits where adhesion to flexible substrates is required.
The inventors of the present invention desired to create a thick film getter composition capable of controlling humidity levels to below about 1000 ppm while at the same time allowing quick processing speeds, of about 5 seconds, and low processing temperatures.
The present invention provides curable thick film getter composition(s), method(s) of controlling moisture, and article(s) formed from those compositions and/or methods which may be used in moisture sensitive devices, including electronic devices which often require humidity control to levels below about 1000 ppm and sometimes below even 100 ppm. Furthermore, it allows for high speed processing of the getter composition and does not require high firing temperatures, rather the composition may be cured by exposure to actinic radiation, including ultraviolet radiation.